Heterogeneous Reaction of Peroxyacetyl Nitrate on Real-World PM2.5 Aerosols: Kinetics, Influencing Factors, and Atmospheric Implications

The formation and decomposition of peroxyacetyl nitrate (PAN), an important atmospheric nitrogen oxide reservoir, can impact the level and cycling of free radicals and nitrogen compounds in the atmosphere. PAN sinks are poorly understood, highlighting the importance of elucidating the heterogeneous reaction of PAN on aerosol surfaces. Here, we report for the first time the uptake behavior, kinetics, and potential mechanism of PAN uptake on real-world aerosol PM_2.5 using a flow tube system. The uptake coefficients (γ) of PAN increased non-linearly from (1.5 ± 0.7) × 10^-5 at 0% relative humidity (RH) to (9.3 ± 2.0) × 10^-5 at 80% RH. The γ decrease with increasing initial PAN concentration is consistent with the Langmuir-Hinshelwood mechanism. Organic components of aerosols may promote heterogeneous loss of PAN through redox reactions. Higher γ occurs with higher water content, lower pH, and lower ionic strength in the aqueous phase of aerosols. The present study suggests that heterogeneous reaction of PAN on ambient aerosols plays a non-negligible role in the atmospheric PAN budget and provides new insights into the role of PAN in promoting atmospheric oxidation capacity during hazy periods with cold and wet weather conditions.

Heterogeneous reaction of peroxyacetyl nitrate (PAN) on soot

The interaction between photochemical oxidants and aerosol particles has been examined in previous atmospheric pollution studies. The heterogeneous reaction can affect the concentration of gases and free radicals, as well as the morphology and properties of particles. In this report, the interaction between the photochemical oxidant peroxyacetyl nitrate (PAN) and soot particles was investigated using a flow tube system. We used real-time online monitoring equipment to track changes in PAN concentrations. Substances on the soot surface were detected using ion chromatography (IC), x-ray photoelectron spectroscopy (XPS), and other surface analysis methods. At 295 K, the upper and lower limits of the initial uptake coefficients were 1.28 × 10^-5 and 9.16 × 10^-9, respectively. The heterogeneous reaction of PAN on soot was a first-order reaction to PAN under both dry and wet conditions. The products formed on soot included CH₃COO^-, HCOO^-, NO₂^-, and NO₃^-. With an increase in relative humidity, the production of all species decreased and the relative amounts changed.

Measurement of trace atmospheric species by chemical ionization mass spectrometry: speciation of reactive nitrogen and future directions

Chemical ionization mass spectrometry (CIMS) has proven to be a powerful method for sensitive, fast time response (t approximately 1 sec) measurements of various atmospheric compounds with limits of detection (LOD) of the order of tens of pptv and lower. The rapid time response of CIMS is particularly well suited for airborne measurements and its application has largely grown out of airborne measurements in the stratosphere and upper troposphere. This work reviews some of the advances in CIMS technology that have occurred in the past decade. In particular, CIMS methods for selective measurement of reactive nitrogen species (e.g., HNO3, HO2NO2, PAN, and NH3) in the lower atmosphere (altitudes approximately 0-8 km) are described. In addition, recent developments in CIMS technology for the selective measurement of gas-phase hydroperoxides and aerosol chemical composition are briefly described.